At the very top, where it says File, Edit, Mail, Community,etc., click on the one that says Mail. There will be a drop-down box. If you look at this list, you should see Address Book.
DON'T PRESS ADDRESS CARD, THAT WILL BE VERY CONFUSING IF YOU DON'T KNOW HOW TO ADD AN EMAIL ADDRESS YET. A window will come up that says Address Book. There will be a list near the bottom that says Send Mail, CC, BCC, Edit, Delete, and Add. Click on Add. Another window will come up that says New Contact. Just fill in the info there, and hit save.